We report for the first time that cultured lens epithelial cell layers and rabbit lenses in vitro transport fluid. Layers of the alphaTN4 mouse cell line and bovine cell cultures were grown to confluence on permeable membrane inserts. Fluid movement across cultured layers and excised rabbit lenses was determined by volume clamp (37 degrees C). Cultured layers transported fluid from their basal to their apical sides against a pressure head of 3 cmH2O. Rates were (in microliter. h-1. cm-2) 3.3 +/- 0.3 for alphaTN4 cells (n = 27) and 4.7 +/- 1.0 for bovine layers (n = 6). Quinidine, a blocker of K+ channels, and p-chloromercuribenzenesulfonate and HgCl2, inhibitors of aquaporins, inhibited fluid transport. Rabbit lenses transported fluid from their anterior to their posterior sides against a 2.5-cmH2O pressure head at 10.3 +/- 0.62 microliter. h-1. lens-1 (n = 5) and along the same pressure head at 12.5 +/- 1.1 microliter. h-1. lens-1 (n = 6). We calculate that this flow could wash the lens extracellular space by convection about once every 2 h and therefore might contribute to lens homeostasis and transparency. (+info)
Effects of dauricine, quinidine, and sotalol on action potential duration of papillary muscles in vitro.
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AIM: To compare the characteristics of dauricine, sotalol, and quinidine on action potential duration (APD). METHODS: Using intracellular microelectrode method to record APD in guinea pig papillary muscles. RESULTS: Dauricine 20 mumol.L-1 prolonged action potential at 90% repolarization, the percent of APD prolongation were 22 +/- 8, 11 +/- 6, 9 +/- 5, 7 +/- 5, 6 +/- 3, 4.3 +/- 2.8, 4.5 +/- 2.8 at the cycle lengths of 200-2000 ms, dauricine became more effective in lengthening APD at short cycle lengths. The effect of dauricine on prolonging APD exhibited normal use-dependence, whereas quinidine 1 mumol.L-1 and sotalol 10 mumol.L-1 were less effective in lengthening APD at short cycle lengths. The effect of quinidine and sotalol on APD exhibited reverse use-dependence. CONCLUSSION: The effect of dauricine on APD depends on activation frequency. (+info)
In vitro metabolism of quinidine: the (3S)-3-hydroxylation of quinidine is a specific marker reaction for cytochrome P-4503A4 activity in human liver microsomes.
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The aim of this study was to evaluate the (3S)-3-hydroxylation and the N-oxidation of quinidine as biomarkers for cytochrome P-450 (CYP)3A4 activity in human liver microsome preparations. An HPLC method was developed to assay the metabolites (3S)-3-hydroxyquinidine (3-OH-Q) and quinidine N-oxide (Q-N-OX) formed during incubation with microsomes from human liver and from Saccharomyces cerevisiae strains expressing 10 human CYPs. 3-OH-Q formation complied with Michaelis-Menten kinetics (mean values of Vmax and Km: 74.4 nmol/mg/h and 74.2 microM, respectively). Q-N-OX formation followed two-site kinetics with mean values of Vmax, Km and Vmax/Km for the low affinity isozyme of 15.9 nmol/mg/h, 76.1 microM and 0.03 ml/mg/h, respectively. 3-OH-Q and Q-N-OX formations were potently inhibited by ketoconazole, itraconazole, and triacetyloleandomycin. Isozyme specific inhibitors of CYP1A2, -2C9, -2C19, -2D6, and -2E1 did not inhibit 3-OH-Q or Q-N-OX formation, with Ki values comparable with previously reported values. Statistically significant correlations were observed between CYP3A4 content and formations of 3-OH-Q and Q-N-OX in 12 human liver microsome preparations. Studies with yeast-expressed isozymes revealed that only CYP3A4 actively catalyzed the (3S)-3-hydroxylation. CYP3A4 was the most active enzyme in Q-N-OX formation, but CYP2C9 and 2E1 also catalyzed minor proportions of the N-oxidation. In conclusion, our studies demonstrate that only CYP3A4 is actively involved in the formation of 3-OH-Q. Hence, the (3S)-3-hydroxylation of quinidine is a specific probe for CYP3A4 activity in human liver microsome preparations, whereas the N-oxidation of quinidine is a somewhat less specific marker reaction for CYP3A4 activity, because the presence of a low affinity enzyme is demonstrated by different approaches. (+info)
Pseudo second degree atrioventricular block with bradycardia. Successful treatment with quinidine.
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Pseudo second degree atrioventricular block resulting from blocked His premature beats was successfully treated with quinidine. The diagnosis was proved by His bundle electrogam which showed both blocked and conducted His premature beats. The blocked His prematures produced second degree atrioventricular block by making the atrioventricular junction refractory. Quinidine abolished both conducted and blocked His extrasystoles. There has been no recurrence of arrhythmia during a one-year follow-up. (+info)
Novel membrane transporter OCTN1 mediates multispecific, bidirectional, and pH-dependent transport of organic cations.
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In the present study, functional characteristics of organic cation transporter (OCTN)1, which was cloned as the pH-dependent tetraethylammonium (TEA) transporter when expressed in mammalian human embryonic kidney (HEK)293 cells, were further investigated using Xenopus oocytes as well as HEK293 cells as gene expression systems. When OCTN1-derived complementary RNA was injected into Xenopus oocytes, pH-dependent transport of [14C]TEA was observed as the same in HEK293 cells. In contrast, a replacement of sodium ions with potassium ions in the surrounding medium did not cause any change in [14C]TEA uptake in Xenopus oocytes expressed with OCTN1. In addition, when OCTN1 was expressed in HEK293 cells, efflux of TEA from the cells was pH dependent, with an accelerated rate at acidic external medium pH. Accordingly, membrane potential or sodium ions are suggested to have no influence on [14C]TEA transport and the transport activity of OCTN1 is directly affected by pH itself. Furthermore, addition of the unlabeled TEA in external medium enhanced the efflux of preloaded [14C]TEA. These observations suggest that OCTN1 is a pH-dependent and bidirectional TEA transporter. OCTN1-mediated [14C]TEA uptake was inhibited by various organic cations such as cimetidine, procainamide, pyrilamine, quinidine, quinine, and verapamil. In addition, uptakes of cationic compounds such as [3H]pyrilamine, [3H]quinidine, and [3H]verapamil and zwitterionic L-[3H]carnitine were increased by expression of OCTN1 in Xenopus oocytes. Accordingly, OCTN1 was functionally demonstrated to be a multispecific and pH-dependent organic cation transporter, which presumably functions as a proton/organic cation antiporter at the renal apical membrane and other tissues. (+info)
Effects of a novel cardioprotective drug, JTV-519, on membrane currents of guinea pig ventricular myocytes.
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We investigated effects of a novel cardioprotective drug, JTV-519 (4-[3-(4-benzylpiperidin-1-yl)propionyl]-7-methoxy-2,3,4,5-tetrahy dro-1,4-benzothiazepine monohydrochloride) on membrane currents of guinea pig ventricular myocytes by whole-cell voltage and current clamp methods. The fast Na+ current (iNa) was activated by ramp pulses from various holding potentials of -90, -80 or -60 mV to 10 mV with various intervals. At 0.2 Hz, JTV-519 inhibited iNa in a concentration-dependent manner with an IC50 of approximately 1.2 and 2 microM at the holding potential of -60 and -90 mM, respectively, implicating a voltage-dependent block. Increasing the pulse frequency from 1 to 2 or 3.3 Hz in the presence of 1 microM JTV-519 shortened the time-course and increased the level of iNa block, indicating a frequency-dependent block. The time-course of iNa blocking by JTV-519 was slower than that of lidocaine and similar to that of quinidine. Ca2+ current (iCa) and the inwardly rectifying K+ current (iK1) were also inhibited by JTV-519. JTV-519 decreased the duration and the height of the plateau of the action potential. We conclude that JTV-519 has frequency- and voltage-dependent blocking effects on iNa as well as inhibition of iCa and iK1. (+info)
Alkalinization-induced K+ current of the mouse megakaryocyte.
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We have recently found that mouse megakaryocytes responded to extracellular alkalinization to pH > 8.0, generating a K+ current under voltage-clamped conditions with the whole cell recording mode of the patch-clamp technique. The purpose of this study was to physiologically and pharmacologically characterize the alkaline-dependent K+ conductance of the megakaryocyte membrane. The alkalinization-induced K+ current (I(ALK)) did not seem to be Ca2+-dependent since I(ALK) was allowed to be generated under intracellularly Ca2+-buffered conditions with 10 mM EGTA, which completely prevented the generation of caffeine-induced Ca2+-activated currents of mouse megakaryocytes; and no [Ca2+]i elevation was evoked by the alkalinization protocol in contrast to a significant increase in [Ca2+]i in response to caffeine when [Ca2+]i was measured with a fura 2 ratiometry. I(ALK) was strongly suppressed with tetraethylammonium (TEA), 4-aminopyridine (4-AP) and streptomycin (SM), but was completely resistant to quinidine (QND). The values of IC50 for the suppression of I(ALK) with TEA, 4-AP and SM were 5.6, 0.47 and 1.5 mM, respectively. Voltage-gated K+ currents (I(K)) of the same megakaryocyte preparation were weakly suppressed with TEA and 4-AP, while they were significantly suppressed with either SM or QND. These results suggest that mouse megakaryocytes possess K+ conductance that was activated by extracellular alkalinization and that probably differs from conventional K+ conductance in its pharmacological properties. (+info)
Enhancing effects of salicylate on tonic and phasic block of Na+ channels by class 1 antiarrhythmic agents in the ventricular myocytes and the guinea pig papillary muscle.
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OBJECTIVE: To study the interaction between salicylate and class 1 antiarrhythmic agents. METHODS: The effects of salicylate on class 1 antiarrhythmic agent-induced tonic and phasic block of the Na+ current (INa) of ventricular myocytes and the upstroke velocity of the action potential (Vmax) of papillary muscles were examined by both the patch clamp technique and conventional microelectrode techniques. RESULTS: Salicylate enhanced quinidine-induced tonic and phasic block of INa at a holding potential of -100 mV but not at a holding potential of -140 mV; this enhancement was accompanied by a shift of the hinfinity curve in the presence of quinidine in a further hyperpolarized direction, although salicylate alone did not affect INa. Salicylate enhanced the tonic and phasic block of Vmax induced by quinidine, aprindine and disopyramide but had little effect on that induced by procainamide or mexiletine; the enhancing effects were related to the liposolubility of the drugs. CONCLUSIONS: Salicylate enhanced tonic and phasic block of Na+ channels induced by class 1 highly liposoluble antiarrhythmic agents. Based on the modulated receptor hypothesis, it is probable that this enhancement was mediated by an increase in the affinity of Na+ channel blockers with high lipid solubility to the inactivated state channels. (+info)